1. Field of the Invention
The present invention relates to ophthalmic photographic apparatuses for use in ophthalmic hospitals.
2. Description of the Related Art
In order to align a subject""s eye (eye under examination) and a photographic apparatus, a fundus camera projects marks so that an image reflected from the cornea can be formed substantially conjugate to the fundus of the eye. The image reflected from the cornea and an image of the fundus are displayed on a monitor and are observed. The fundus camera is positioned so that the image reflected from the cornea can be in focus and be displayed symmetrically relative to the center of the monitor.
In the foregoing known example, the following problems occur:
(1) In general, fundus photography in group examination is performed by aligning the approximate central point between the optic disk (discus nervi optici) and the macula lutea to be at the center of the photographic screen. Since the field angles of the optic disk and the macula lutea are separated from each other by approximately 18 degrees, this photographic method captures images with a tilt of approximately 9 degrees.
The eyeball optical system has rotation symmetry with respect to the optical axis between the approximate center of the pupil and the macula lutea. Capturing an image eccentrically means that the image is captured while decentering the eyeball. As a result, one side of the image tends to become flared. When a visual field diaphragm is reduced to avoid flare, the photographic field angle becomes narrow.
(2) In the known method, images are captured from an eccentric position relative to the center of the pupil. When capturing an image of a subject""s eye having the pupil with a small diameter, the fundus of the eye cannot be illuminated uniformly.
In order to solve the foregoing problems, it is an object of the present invention to provide an ophthalmic photographic apparatus for appropriately displaying fixation targets corresponding to a subject""s left and right eyes under examination.
In order to achieve the foregoing objects, according to the present invention, an ophthalmic photographic apparatus is provided including a mark projecting unit for projecting a mark onto a cornea of an eye under examination; an observation unit for observing a reflected image of the mark and an image of a fundus of the eye; a left-right detecting unit for detecting whether the eye under examination is the left eye or the right eye; and a control unit for displaying, on the observation unit, the reference mark for aligning the reflected image of the mark at different positions corresponding to the left and right eyes in accordance with information detected by the left-right detecting unit.
As described above, an ophthalmic photographic apparatus according to the present invention includes a determination unit for determining whether a subject""s eye (eye under examination) is the left eye or the right eye, and reference marks for alignment are presented at eccentric positions in accordance with the determination. Thus, the following advantages can be achieved:
(a) Since flare-free, satisfactory images can be obtained, the image capturing and reading efficiency can be improved;
(b) With tolerance to flare, images can be simultaneously taken at wide field angles, and the diagnosis efficiency can be further improved; and
(c) Since images can be taken from the center of the pupil, satisfactory images of the fundus of a subject""s eye having a small-diameter pupil can be captured.
Further objects, features, and advantages of the present invention will become apparent from the following description of the preferred embodiments with reference to the attached drawings.